This invention concerns off highway dump trucks of the type having rear dumping bodies. More specifically, the invention deals with automatic tailgates that pivot around a pivot point on the dump body when the body is hoisted to a dumping mode.
Prior art automatic tailgates are well known in the industry. Automatic tailgates have been in use since the advent of horse drawn dumping bodies. Even with this extensive prior art, no automatic tailgates are known that have the advantages and features of the instant tailgate.
It is old in the art to close off the extreme end of a dump body with a tailgate. The tailgate prevents the spilling of the load and allows for better utilization of the capacity of the truck load carrying body. Avoiding spillage on a haul road is important as this minimizes the maintenance of the haul road and may prevent undesirable damage to the rubber tires of most dump trucks. Clean roads also allow higher speeds and the attendant higher productivity.
Automatic tailgates that swing up and away from the open end of a dump body typically operate automatically as the dump body is pivoted to dump. This allows the operator to stay in the cab when dumping. Also, since the tailgate swings relatively upwardly the tailgate is clear of the material being dumped. It won't prevent the material from being discharged and will not become jammed with the material as may happen with a tailgate that is hinged at the end of the body.
This embodiment of automatic tailgate has all the features and advantages mentioned above as well as several items that make this invention an advance over the prior art.
One advantage of this invention is that it prevents an unbalanced distribution of the load being carried in the body. A dump truck is designed to have a specified weight distribution when fully loaded. For instance, in the embodiment shown the ideal loaded weight distribution is to have fifty percent of the load over the front wheels and fifty percent over the back wheels. Since most dump trucks of this type are not designed to have tailgates, the body design will yield this fifty-fifty proportion. If a tail-gate is fitted to the end of the body however, the load center will not only move vertically, but will also move horizontally toward the rear of the body and thus grossly affect the weight distribution. This unbalanced and undesigned for condition leads to abnormal stress and strain on the rear axle and components thus increasing the wear factor and the chance of failure. With the instant invention, the tailgate proper is located inboard of the extreme end of the body by a distance of several feet. The actual location is a predetermined location found so that as the load is increased due to the extra height given to the end of the body by the tailgate, the load center remains vertically above the optimum load center of the original design. Thus, the originally preferred fifty-fifty weight distribution between axles can be maintained.
Notice that in the preferred embodiment a fifty-fifty load distribution is considered optimum. Other embodiments where other proportions are desired, such as 40-60, would also benefit from this invention. The idea is to maintain the optimum load center on the same vertical center line corresponding to the original design.
Another advantage of this invention is that since the tailgate is carried inboard of the extreme end of the body, any spillage caused by jostling while traveling on the haul road will fall over the tailgate into the pan at the back section of the body. This will minimize the deterioration of the haul road due to extraneous material and will reduce grading frequency and tire damage.
Also an advantage of this invention is that since the tailgate fits inside the body, the spreading of the body when loaded will not prevent the tailgate from swinging into position inside the body. In one prior art device, the tailgate is designed to telescope within itself to accommodate the spreading body sides. This costly and bothersome modification isn't necessary with the instant tailgate.
A further advantage of this invention is that since the tailgate fits into the body, it can be equipped with a cutting edge that will slice through any residual dirt or mud that has stuck in the body thus allowing good sealing between the lower edge of the tailgate and the body floor. The effectiveness of this cutting edge can be improved by using a solid link to actuate the tailgate support arm in place of a preferred flexible cable. The solid linkage will force the cutting edge to the floor of the body.
An object of this invention is to provide a tailgate that can be fitted to a current production dump truck without modifying the basic equipment of the truck. The automatic tailgate should also be easy to manufacture and install, as this tailgate is.
Another object of this invention is to provide an automatic tailgate that can be easily removed when it is not needed or when servicing of the vehicle requires access to areas behind the tailgate apparatus.
Also an object of this invention is to provide a modification to a dump truck that enables the truck to be used in hauling slurry material without the material sloshing out the back of the body.